Biosynthesis and Properties of Poly(3-hydroxybutyrate-c o-3-hydroxyhexanoate) Polymers

• Published in: Biomacromolecules Vol. 3; no. 5; pp. 1006 - 1012
• Main Authors: Asrar, Jawed, Valentin, Henry E, Berger, Pierre A, Tran, Minhtien, Padgette, Stephen R, Garbow, Joel R
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 01.09.2002
• Subjects: 3-Hydroxybutyric Acid - chemistry; 3-Hydroxybutyric Acid - metabolism; Aeromonas hydrophila; Aeromonas hydrophila - metabolism; Biocompatible Materials - chemistry; Biocompatible Materials - metabolism; Caproates - chemistry; Caproates - metabolism; Crystallization; Fermentation; Magnetic Resonance Spectroscopy; Materials Testing; Pseudomonas putida; Pseudomonas putida - metabolism; Stress, Mechanical; Temperature
• ISSN: 1525-7797; 1526-4602
• DOI: 10.1021/bm025543a

In support of programs to identify polyhydroxyalkanoates with improved materials properties, we report on our efforts to characterize the mechanical and thermal properties of copolyesters of 3-hydroxybutyrate (3HB) and 3-hydroxyhexanoate (3HHx). The copolyesters, having molar fraction of 3HHx ranging from 2.5 to 35 mol % and average molecular weights ranging from 1.15 × 105 to 6.65 × 105, were produced by fermentation using Aeromonas hydrophila and a recombinant strain of Pseudomonas putida GPp104. The polymers were chloroform extracted and characterized by solution-state and solid-state nuclear magnetic resonance (NMR) spectroscopy and a variety of mechanical and thermal tests. Solution-state 1H NMR data were used to determine polymer composition-of-matter, while solution-state 13C NMR data provided polymer-sequence information. Solvent fractionation and NMR spectroscopic characterization of these polymers showed that polymers containing up to 9.5 mol % 3HHx had a Bernoullian compositional distribution. By contrast, polymers containing more than 9.5 mol % 3HHx had a bimodal polymer composition. Solvent fractionation of these 3HHx-rich polyesters produced two polymer fractions, each of which was again consistent with Bernoullian polymerization statistics. Solid-state NMR relaxation experiments provided insight into aging in poly(3HB- co-3HHx) copolymers, demonstrating increased polymer-chain motion with increasing 3HHx content. The elongation-to-break ratio in the polyesters increased with increasing molar fraction of 3HHx monomers. Aging properties of the poly(3HB- co-3HHx) copolymers were very similar to copolymers of 3HB and 3-hydroxyvalerate (3HV). However, poly(3HB- co-3HHx) exhibited increased activation energy to thermal degradation with increasing 3HHx content.